The processing steps of roughening, thermal coating and honing are used for manufacturing tribologically suitable surfaces in cylinder bores of combustion engines. The roughening has the purpose of creating an adequate topography on the substrate surface, which enables secure connection between the thermal sprayed coating and the substrate. The design of the profile form and the profile depth has an essential influence on the bonding tensile strength of the coating. The coating bonding per se is determined by the adhesion between the two materials, the lateral shrinkage strains resulting between the form elements of the roughening profile and the embedded coating, and the radial form fit resulting due to undercuts of the convex roughing profile elements.
The invention concerns a tool and a method for mechanically roughening a substrate surface so that a coating with very good adhesion can be applied to the substrate surface prepared according to the invention. In addition to other methods, such as sand blasting, laser blasting or high-pressure water blasting, methods of mechanical machining are known, wherein chipping and forming are combined with each other in terms of process technology. This latter group, in turn, includes processes which apply chipping and pressing involving a sliding process between the pressing tool and the material. A further combination of chipping and forming consists in chipping with subsequent rolling, wherein the surface profile that is initially generated by fine boring, rotating or milling is formed by rollers rolling over and forming the substrate surface, thereby improving the bonding characteristics.
As the invention is concerned with the last-mentioned combination of chipping and rolling (or tumbling), prior art is taken into consideration below.
EP 2 267 178 A2 describes a roughening method using a combination of chipping and rolling. The rolling operation is designed such that, with the combination tool, the distance between the roller and the form blade is dependent on the periodicity of the form profile (bridge, breadth and feed) cut in the first method step. Each roller covers one profile bridge.
The axial arrangement of the chipping tool and the roller is dependent on the form blade and its kinematic conditions, such as feed, bridge breadth, profile depth. This requires exact adjustment of the working surfaces of the blade and the roller with respect to each other. As the roller always machines only one bridge breadth, a short tool life of the roller must be expected. Furthermore, the roller is not readjustable relative to the blade in a radial direction so that, with varying wear rates, readjustment is no longer possible and the degree of forming is thereby reduced, with smaller undercuts being produced.
DE 10 2006 004 769 A1 is based on a roughening method, in which the substrate surface is chipped in a first method step and the previously chipped profile tips are “bent” in a subsequent step. This can be performed by means of rolling, pressing or blasting. For this reason, the substrate surface, i.e. the subsequent contact surface for the coating, is a profile form with undercuts. The roller is not slanted orthogonally with respect to the chipped profile, so that slippage occurs between the roller and the chipped profile.
DE 10 2008 024 313 A1 also discloses roller machining after cutting. However, the roller is designed with numerous knife discs, the cutting edges of which are arranged at a distance of the profile bars. This design has the substantial disadvantage that the tool must initially be exactly aligned to the profile tip position of the pre-machined profile form in the axial position, in order to then split the profile at these convex profile bridges by means of radial feed. Furthermore, it is necessary to exactly adjust the distance of the knife discs to the feed and the distance of the raised bridges. Also in this case, the rolling tool is profile-oriented with respect to the axial position and design, which results in complex handling for the process and also complex production as far as the distancing of the knife discs is concerned.
DE 20 2009 014 180 U1 also combines a chipping process with a rolling process for forming the profile bridges. In this method, the roller must be provided with a profiling based on the feed and the distance of the profile bridges. These tools are subject to high wear on the roller side, so that economical operation is not possible. The axial distancing of the contours of the roller from the form blade also requires substantial effort during installation of the tool.
All above-mentioned methods require tools that are difficult to manufacture and to adjust and are subject to relatively great wear, and some of which cannot be readjusted and therefore complicate or obstruct economical and reliable large-scale production.
It is the underlying purpose of the invention to provide a device and a method for mechanical roughening, which can be used independently of the subsequent coating method. The inventive device can thereby be used on a honing machine as well as on a machining center. In dependence on the material and the profile geometries, minimum quantity lubrication or heavy lubrication should both be possible.